Preparation of photographic emulsions



United States Patent Office 3,241,970 Patented Mar. 22, 1966 3,241,970 PREPARATION OF PHOTGGRAlI-HC EMULSIONS Stanley P. Popeck, Nimmonsiiurg, N .Y., assignoito General Aniline & Film Corporation, New York, N.Y., a

corporation of Delaware No Drawing. Filed Oct. 6, 1961, Ser. No. 143,290

' 11 Claims. (Cl. 9694) This invention relates to a novel process for the preparation of silver halide photographic emulsions. More particularly, this invention relates to a novel process for the preparation of silver bromide, silver iodide and mixed silver bromide-silver iodide photographic emulsions.

The prior art processes for the preparation of silver halide emulsions involve the addition of a silver nitrate, or ammoniacal silver nitrate, solution to an equeous solution of an alkali halide, or mixed alkali halides, containing a protective colloid. These processes suffer from many disadvantages due to the fact that the concentration of the halides continuously changes as the precipitation of the silver halide is progressing. The continuous change in halide concentration leads to an undesirable effect since the silver halides are soluble in the alkali halides which are present in a large excess at the start of the precipitation and gradually diminish as the precipitation pro gresses. This variation in solubility influences the formation of complex silver salts which in turn impair the quality of the photographic emulsion. Additionally, the continuous change in halide concentration during the precipitation of the silver halide atfects the formation of mixed crystals so that an elfective degree of control is rendered extremely diflicult.

Therefore, it is the object of this invention to provide a novel process for the preparation of silver halide photographic emulsions, said process being able to maintain the concentration of excess halide substantially constant throughout the entire precipitation time of the silver halide.

It is also an object of the invention to provide a process for the preparation of silver halide photographic emulsions which is efficient, easy to control and capable of yielding photographic emulsions of a high degree of quality.

It has now been discovered that the above objects can be obtained by forming a complex of silver bromide, silver iodide, or a mixture of the two, with a normally liquid nitrogen containing solvent capable of forming complexes with gold and silver salts, and then adding this complex to a suitable solvent which may optionally contain a protective colloid.

The instant invention is based on the discovery that silver bromide, silver iodide, or mixtures of the two, complex with the aforesaid solvent in the presence of excess bromide ions. The complex is soluble in the solvent up to 20% by weight. The solution of this complex is colorless and is not sensitive to light. It should become immediately obvious that such a complex is particularly adapted to the photographic emulsion art when the silver halide or halides can be made to precipitate out of the complex onto a suitable carrier so that they will become light sensitive again.

The complex is conveniently prepared simply by adding silver bromide, silver iodide or mixtures of the two to the normally liquid nitrogen containing solvent in the presence of excess bromide ions and stirring. Suitable solvents for my purpose are dimethyl forrnamide, pyrrolidone, pyriconvenient source of bromide ions is hydrobromic acid so that this acid is preferred as a bromide source.

As has been previously pointed out, the photographic emulsions can be prepared simply by adding the silver halide complex to a suitable carrier contained in a material which acts both as a solvent for the carrier and as a precipitate for the complex. The solvent-precipitants which can be employed include water, the lower molecular weight aliphatic alcohols, i.e. methanol, propanol, iso propanol, butanol, amyl alcohol and other organic solvents which are miscible with the normally liquid nitrogen containing complexing agent. The preferred solvents are water and aliphatic alcohols of from 1-5 carbon atoms, with water being particularly preferred.

In a modification of this procedure, the complex can be added to the solvent-precipitant which contains dissolved in place of the carrier an anionic, cationic, nonionic or amphoteric dispersing agent such as sodium lauryl sulfate, iso-octyl phenoxy polyoxyethylene ethanol, sodium N-methyl N-oleoyl taurate, sodium N-lauroyl sarcosinate. Upon addition of the complex to this solution, the complex is broken, silver halide is reformed but stays dispersed in the solvent-precipitant. This dispersion is subsequently admixed with a colloidal carrier material such as gelatin or polyvinyl alcohol to form the light sensitive silver halide emulsion.

My invention offers the special advantage that all operations up to the re-precipitation can be carried out in full light, only the subsequent steps requiring the use of a dark room.

The following examples will illustrate the instant invention.

EXAMPLE I Boiled type emulsions A mixture of 32.7 grams of silver bromide 1.13 grams of silver iodide were placed in a flask and 55 cubic centimeters of dimethyl formamide were added and the entire mixture was stirred for one minute. 15 cubic centimeters of a 48% aqueous solution of hydrobromic acid was then added with stirring. After the mixture had been stirred, an additional cubic centimeters of dimethyl formamide was added in two portions of 65 cubic centimeters each, with stirring after the addition of each portion. This procedure yielded a complex of dimethyl formamide and mixed silver halides dissolved in dimethyl formarnide.

A mixture of 450 cubic centimeters of water and 3.5 grams of gelatin was placed in a constant temperature bath at 70 C. and stirred. To this was added the complex and the entire mixture was stirred for three minutes. The mixture was ripened for ten minutes, precipitated and washed. After several washings the silver halide crys tals were redispersed at 40 C. by the addition of 48 grams of gelatin dissolved in 475 cubic centimeters of water. The resulting emulsion was after-ripened and coated on a suitable film base.

The resulting emulsion was of excellent quality, was low in fog and was comparable in speed to normal positive type film.

EXAMPLE II Ammonia type emulsion A mixture of 83.0 grams of silver bromide and 1.6 grams of silver iodide was added to 120 cubic centimeters of dimethyl formamide and stirred for one minute. 80 cubic centimeters of a 48% solution of hydrobromic acid was then added with stirring. 300 cubic centimeters of dimethyl formamide was then added in two portions of cubic centimeters each, stirring for a few minutes after the first addition and until dissolved after the second. The resulting complex was then added to a solution maintained at 56 C. of 6.5 grams of gelatin, 260.0 cubic centimeters of water and 70.0 cubic centimeters of a 28% solution of ammonium hydroxide. After stirring for nineteen minutes and digesting for ten minutes, the emulsion was precipitated and washed several times with cold water.

A solution of 48 grams of gelatin in 400 cubic centimeters of water was added and the mixture was stirred until homogeneous. The emulsion was then digested and coated on a film base to produce an excellent quality photographic emulsion of good speed.

It is to be understood that the dimethyl formamide in the examples may be replaced by any other of the enumerated complexing agents, e.g. pyrrolidone, pyridine, butylamine, N-dimethylaniline, dibutylamine, etc.

My invention can also be carried out by dissolving a colloidal carrier material such as gelatin in the solution containing the silver halide complex and adding this solution to the precipitating medium. Instead of pouring the solution of the silver halide complex, which may contain a colloidal carrier, into the liquid precipitating agent, it is also possible to spray the solution of the silver halide complex into a chamber which contains the precipitant in its vapor form. For instance, the solution of the complex may be sprayed into a chamber containing steam. As a modification, the steam can be brought into the chamber flowing in the form of a counter current to the direction of travel of the silver complex spray.

What is claimed is:

1. A process for the preparation of photographic emulsions which comprises adding a silver halide selected from the group consisting of silver bromide, silver iodide and mixtures of the two to a normally liquid organic nitrogen containing solvent in the presence of excess bromide ions so as to form a complex soluble in said solvent, and then adding the resulting solution of said complex to a solution of carrier, the solvents used in the preparation of the carrier solution being miscible with the said nitrogen containing solvent and capable of breaking the complex, thereby forming a dispersion of silver halide in the solution of the carrier.

2. The process of claim 1 wherein the carrier is gelatin.

3. The process as defined in claim 1 wherein the normally liquid nitrogen containing solvent is selected from the class consisting of dimethyl formamide, pyridine, pyrrolidone, N-dimethylaniline, butylamine and dibutyla- 4 mine.

4. The process of claim 1 wherein the solvent used in the preparation of the carrier solution is selected from the group consisting of water and aliphatic alcohols of from 1-5 carbon atoms.

5. A process for the preparation of photographic emulsions which comprises adding mixtures of silver bromide and silver iodide to dimethyl formamide and hydrobromic acid to form a complex soluble in dimethyl formamide and then adding the resulting solution of said complex in dimethyl formamide to an aqueous solution of gelatin.

6. A process for the preparation of photographic emulsions which comprises adding a silver halide selected from the group consisting of silver bromide, silver iodide, mixtures of the two and silver bromoiodide to a normally liquid organic nitrogen containing solvent in the presence of excess bromide ions so as to form a complex soluble in said solvent, and then adding the resulting solution of said complex in said solvent to a solution of surfactant in a solvent miscible with said nitrogen containing solvent, thereby re-forming the silver halide, and admixing to the dispersion thus obtained a colloidal carrier material so as to form a light sensitive silver halide emulsion.

7. A process which comprises adding a silver halide selected from the group consisting of silver bromide, silver iodide and mixtures of the two to dimethyl formamide in the presence of excess bromide ions so as to form a complex soluble in dimethyl formamide.

8. A process which comprises adding a mixture of silver bromide and silver iodide to dimethyl formamide in the presence of hydrobromic acid to form a complex soluble in dimethyl formamide.

9. A process which comprises mixing together silver bromide, dimethyl formamide and hydrobromic acid so as to form a complex soluble in dimethyl formamide.

10. A process which comprises mixing together silver iodide, dimethyl formamide and hydrobromic acid so as to form a complex soluble in dimethyl formamide.

11. The complex produced by the process in claim 7.

References Cited by the Examiner UNITED STATES PATENTS 2,875,052 2/1959 Weyde 96-94 X 3,031,304 4/1962 Oliver 9694 FOREIGN PATENTS 471,366 9/1937 Great Britain.

OTHER REFERENCES James et 211.: Fund. of Photographic Theory--1960, Morgan & Morgan, Inc., pp. 30-34.

NORMAN G. TORCHIN, Primary Examiner. 

1. A PROCESS FOR THE PREPARATION OF PHOTOGRAPHIC EMULSIONS WHICH COMPRISES ADDING A SILVER HALIDE SELECTED FROM THE GROUP CONSISTING OF SILVER BROMIDE, SILVER IODIDE AND MIXTURES OF THE TWO TO A NORMALLY LIQUID ORGANIC NITROGEN CONTAINING SOLVENT IN THE PRESENCE OF EXCESS BROMIDE IONS SO AS TO FORM A COMPLEX SOLUBLE IN SAID SOLVENT, AND THEN ADDING THE RESULTING SOLUTION OF SAID COMPLEX TO A SOLUTION OF CARRIER, THE SOLVENTS USED IN THE PREPARATION OF THE CARRIER SOLUTION BEING MISCIBLE WITH THE SAID NITROGEN CONTAINING SOLVENT AND CAPABLE OF BREAKING THE COMPLEX, THEREBY FORMING A DISPERSION OF SILVER HALIDE IN HE SOLUTION OF THE CARRIER. 